present invention relates generally to selectively aspirating styler assemblies; and particularly relates to such stylet assemblies having selectively controllable flow paths such as may be used, for example, to optimally facilitate the introduction of a catheter, shunt or cannula into a parenchymatous organ or structure. The present invention also has application in connection with other procedures, such as the placement of a cannula within the body for locating a wire lead or electrode, or otherwise establishing a fluid flow path or placing an elongated tubular member between first and second locations outside and within the body, respectively.
The stylet assembly of the present invention defines a fluid flow path, allowing pressure at the inserted distal end of the stylet to be controlled to permit regulation of aspiration of tissue or fluid into the catheter or shunt during withdrawal of the stylet. As an example, one primary application of this invention involves intracerebral ventricular (ICV) catheter placement. Establishing a fluid flow path through the stylet and avoiding aspiration of tissue into the catheter requires a mechanism to prevent the creation of a vacuum while withdrawing the stylet from the catheter. However, the present invention also may be used under circumstances in which some aspiration is desired, as in the case of a biopsy from a localized area.
Insertion of a catheter, shunt or cannula into the body is often accomplished with the use of a solid stylet or guidewire which extends into the catheter to provide sufficient rigidity to facilitate passage along a desired path through body tissue. Once the catheter or shunt is properly positioned, and possibly during the positioning procedure itself, the stylet must be withdrawn. Pulling a solid stylet from a positioned catheter or shunt device creates a vacuum at the inserted open end of the device. Fluid or tissue or both is drawn into the catheter to fill the vacuum, and the displacement of the tissue may cause undesirable physiologic side effects. In the case of an ICV catheter placement, such a vacuum could result in aspiration of choroid plexus into the catheter, resulting in extreme tissue damage proximate the catheter.
Hollow stylets have been known previously. For example, U.S. Pat. No. 5,098,411 issued to Watson, discloses a hollow stylet. Such hollow stylets offer an advantage over solid ones in that they allow fluid to exit. Hollow stylets may thus be utilized to determine, through fluid return, when a desired location in the brain or other organ is reached. A specific problem during catheter placement, however, is that tissue can be "cored" in the distal opening if an open-ended hollow catheter/stylet or cannula/stylet assembly is used, and tissue can intrude through apertures in the catheter even if the assembly is not open-ended. Additionally, hollow catheter/stylet and cannula/stylet assemblies, although solid, may not have optimal rigidity, making placement within the body difficult.
Accordingly, the present invention provides new methods and apparatus for overcoming one or more of these deficiencies by providing a stylet defining a flow path which may be selectively opened or closed to optimize the rigidity of the stylet while minimizing tissue damage proximate an outer tubular member placed through use of the stylet.